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A researcher with the Pacific Northwest National Laboratory collects samples from Sequim Bay, Washington that will be analyzed for total alkalinity and dissolved inorganic carbon measurements during the February 2025 alkalinity release experiment. Credit: Nick Ward, PNNL
Savoie, A.M., M. Ringham, C. Torres Sanchez, B.R. Carter, S. Dougherty, R.A. Feely, D. Hegeman, J. Herndon, T. Khangaonkar, J. Loretz, T. Minck, T. Pelman, L. Premathilake, C. Subban, J. Vance, and N.D. Ward (2025): Novel field trial for ocean alkalinity enhancement using electrochemically derived aqueous alkalinity. Front. Environ. Eng., 4, 1641277, doi: 10.3389/fenve.2025.1641277.
Carefully enhanced wastewater could one day benefit coastal marine resources
The continual rise of carbon dioxide in the atmosphere isn't just changing weather patterns, it's also silently altering the chemistry of the global ocean. As CO2 dissolves into seawater, it forms carbonic acid, driving down ocean pH in a process known as ocean acidification. This fundamental shift threatens marine economies, ecosystems, and organisms from shellfish to coral reefs.
One potential approach for reducing the local effects of ocean acidification is called ocean alkalinity enhancement, which involves shifting the chemistry of ocean water back toward its natural, slightly alkaline (basic) state. Over the past two years, a small-scale research project in Sequim, Washington has explored whether a new electrochemical process could make seawater locally less acidic while enabling it to absorb more carbon dioxide from the atmosphere. The project is part of NOAA's larger exploration of emerging ocean carbon management technologies, which it is pursuing at the direction of Congress.
The findings of the research team, which included scientists from NOAA's Pacific Marine Environmental Laboratory and the University of Washington, the Department of Energy's Pacific Northwest National Laboratory (PNNL), and the company Ebb Carbon, were published in the journal Frontiers in Environmental Engineering.
"Our project was about implementing the method in a highly-controlled, contained, modeled, and monitored environment," said Brendan Carter, a scientist with the NOAA-University of Washington Cooperative Institute for Climate, Ocean, and Ecosystem Studies. "Our two federal labs and Ebb Carbon teamed up to ensure that this process was safe and had the expected impacts on the chemistry of seawater when operated on small scales."
The three-year project involved pumping small amounts of seawater from Washington's Sequim Bay into PNNL's Marine and Coastal Research Laboratory. The seawater then entered Ebb's prototype bipolar membrane electrodialysis system, which passed it through a series of electrically-charged membranes that split seawater into alkaline and acidic streams.
The treated alkaline seawater was held in open-air tanks while scientists measured the partial pressure of carbon dioxide dissolved in the seawater, pH, turbidity, dissolved oxygen, total dissolved inorganic carbon, and total alkalinity. The treated seawater was returned to the ocean through PNNL's existing wastewater system in accordance with existing permits.
The researchers conducted two experiments, one in November 2024 and the second in February 2025. Their primary objectives were to assess their ability to maintain and monitor the elevated pH (less acidic) within the facility, ensuring it remained below the permitted maximum at the end of the pipe, and to determine if the increased alkalinity could be detected beyond the outfall.
In the November trial, about 7,000 gallons of alkalinity-enhanced seawater was released, roughly the volume carried by a large tanker truck. The February trial involved releasing 47,000 gallons of alkalinity-enhanced seawater—a nearly seven-fold increase in the volume of discharged seawater compared to the November pilot. (For comparison, an Olympic swimming pool holds 660,000 gallons.) Still, the team observed no detectable alterations to the surrounding water's temperature, salinity, turbidity, or oxygen levels, indicating a minimal immediate environmental impact. They did observe a very localized increase in alkalinity and pH that dissipated within approximately eight feet of the discharge pipe. This rapid dilution highlighted the challenges of detecting small-scale ocean alkalinity enhancement signals in dynamic coastal environments.
This study demonstrates that a conservative small-scale release of electrochemically generated alkalinity-enhanced seawater from a coastal outfall can meet existing environmental permits, and temporarily improve water quality. Questions of scale remain to be addressed, however.
Even within cautious thresholds, widespread adoption of ocean alkalinity enhancement through larger municipal or industrial facilities could contribute to increased ocean carbon uptake and provide local or regional ocean acidification mitigation.